Method of vaporizing and combining a liquefied cryogenic fluid stream with a gas stream

ABSTRACT

THE PRESENT INVENTION RELATES TO AN IMPROVED METHOD OF VAPORIZING AND COMBINING A STREAM OF LIQUEFIED CRYOGENIC FLUID, SUCH AS LIQUEFIED NATURAL GAS, WITH A GAS STREAM, SUCH AS NATURAL GAS. THE GAS STREAM IS DIVIDED INTO FIRST AND SECOND PORTIONS, AND THE PRESSURE OF THE FIRST PORTION IS ELEVATED AN AMOUNT SUFFICIENT TO CAUSE IT TO PASS THROUGH A HEATING CIRCUIT AND RECOMBINE WITH THE SECOND PORTION OF THE GAS STREAM. THE FIRST PORTION OF THE GAS STREAM IS HEATED WITHIN THE HEATING CIRCUIT, AND THE STREAM OF LIQUEFIED CRYOGENIC FLUID TO BE VAPORIZED AND COMBINED WITH THE GAS STREAM IS INJECTED DIRECTLY INTO THE HEATED FIRST PORTION WITHIN THE HEATING CIRCUIT SO THAT THE LIQUEFIED CRYOGENIC FLUID IS VAPORIZED AND MIXED WITH THE FIRST PORTION OF THE GAS STREAM. THE RESULTING MIXTURE OF VAPORIZED CRYOGENIC FLUID AND THE FIRST PORTION OF THE GAS STREAM IS THEN COMBINED WITH THE SECOND PORTION OF THE GAS STREAM.

Jan. 29, 1974 E M. ARENSON 3,788,825

METHOD OF VAPORIZING AND COMBINING A LIQUEFIED CRYOGENIC FLUID STREAM WITH A GAS STREAM Filed OOt. 6, 1970 /A/:/:-A/r0/2 50mm 44.. AR/EA/SOA/ I 11 i L B ATTOQA/EYS United States Patent Int. Cl. F1711 1/04 US. Cl. 48-190 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an improved method of vaporizing and combining a stream of liquefied cryogenic fluid, such as liquefied natural gas, with a gas stream, such as natural gas. The gas stream is divided into first and second portions, and the pressure of the first portion 1s elevated an amount suflicient to cause it to pass through a heating circuit and recombine with the second portion of the gas stream. The first portion of the gas stream is heated within the heating circuit, and the stream of liquefied cryogenic fluid to be vaporized and combined with the gas stream is injected directly into the heated first portion within the heating circuit so that the liquefied cryogenic fluid is vaporized and mixed with the first portion of the gas stream. The resulting mixture of vaporized cryogenic fluid and the first portion of the gas stream is then combined with the second portion of the gas stream.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 6,889 filed I an. 29, 1970.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates generally to an improved method of vaporizing and combining a stream of liquefied cryogenic fluid with a gas stream, and more particularly, but not by Way of limitation, to an improved method of vaporizing and combining a stream of liquefied cryogenic fluid with a gas stream wherein the liquefied cryogenic fluid i injected directly into the gas stream.

(2) Description of the prior art Cryogenic fluids exist in a liquid state only at very low temperatures. In many applications, such fluids are stored in the liquid state, and when they are needed, the fluids are vaporized and combined with other gas streams. For example, cryogenic fluids such a liquefied petroleum gas (LPG) andliquefied natural gas (LNG) are commonly used in the supply and distribution of natural gas for carrying out a process known as Peak Shaving. Peak shaving processes are used in area Where natural gas is not locally produced and as a result must be transported by pipeline from remote producing fields. Such pipelines are generally designed for a natural gas capacity below that required during peak consumption period in the area of use. Consequently, during such periods, e.g., prolonged cold spells, the demand for natural gas exceeds the capacity of the pipeline. When this condition exists, the stored LPG or LNG is vaporized, superheated and combined with the natural gas stream to increase the total volume of gas available for use.

A common peak shaving process presently being used by the natural gas producing and distribution companies utilizes LNG. The natural gas pipeline system for continuously transporting a supply of natural gas from remote producing fields to the area of use is sized for a gas capacity between the minimum demand during the summer months and the peak demand during the winter months. A refrigeration system is installed in the area of use, and during the summer month the excess natural gas transported by the pipeline is refrigerated, liquefied and stored. During the winter months the stored liquefied natural gas is revaporized, superheated and combined with the pipeline natural gas so that the peak natural gas demand is met. Heretofore, various types of heating apparatus have been used to preheat, vaporize and superheat LNG prior to combining it with the gas transported through the pipeline system. Such heating apparatus generally require special materials of construct-ion due to the low temperatures encountered. For example, LNG exists in liquid state at a temperature of approximately 260 'F. and as a result, stainless steel or aluminum must be used in the parts of the heating apparatus exposed to the LNG in order to prevent thermal stress failures thereof.

In my copending application, Ser. No. 6,889 filed Ian. 29, 1970, methods are disclosed for vaporizing and combining a liquefied cryogenic fluid stream with a gas stream wherein the use of expensive cryogenic fluid heating apparatus is obviated. Specifically, the gas stream is injected directly into the heated gas stream and intimately contacted therewith thereby causing the cryogenic fluid stream to be vaporized and combined with the gas stream. While these methods are generally highly satisfactory, the resulting combined gas stream is obtained at a substantially lower pressure level than the pressure level of the gas stream prior to combining the cryogenic fluid therewith. That is, a substantial overall drop in the gas stream pressure level is experienced. In certain applications, a pressure reduction of the gas stream constitutes a disadvantage in that additional gas stream compressor horsepower is required to overcome the pressure reduction which constitutes a substantial increase in the operating cost of the pipeline system.

By the present invention, an improved method of vaporizing and combining a liquefied cryogenic fluid stream with a gas stream is provided whereby a substantial gas stream pressure drop is not encountered.

SUMMARY OF THE INVENTION The present invention relates to an improved method of vaporizing and combining a liquefied cryogenic fluid stream with a gas stream comprising the steps of dividng the gas stream into first and second portions, elevatmg the pressure of the first portion an amount sufiicient to cause it to pass through a heating circuit and recombine with the second portion of said gas stream without incurring a substantial drop in said gas stream, heating the first portion of the gas stream Within the heating circuit, injecting the stream of liquefied cryogenic fluid directly-into the heated first portion of the gas stream within the heating circuit so that the liquefied cryogenic fluid is vaporized and mixed with the first portion, and combining the mixture of the first portion of the gas stream and vaporized cryogenic fluid with the second portion of the gas stream.

It is, therefore, a general object of the present invention to provide an improved method of vaporizing and combining a liquefied cryogenic fluid stream with a gas stream.

A further object of the present invention is the provision of an improved method of vaporizing and combining a liquefied cryogenic fluid stream with a gas stream for transport to a point of use wherein expensive and elaborate heating apparatus for vaporizing and superheating the cryogenic fluid is obviated and wherein an overall pressure reduction of the gas stream does not result.

Other and further objects, features and advantages of the invention will be apparent from the following detailed description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of the system for carrying out the method of the present invention,

FIG. 2 is a diagrammatic view of an alternate system for carrying out the method of the present invention, and

FIG. 3 is a side elevational view, partially in section of a contactor apparatus which may be employed in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, and particularly to FIG. 1, a system for carrying out the improved method of the present invention is illustrated, generally designated by the numeral 10. The system basically comprises a conduit 12 for receiving and conducting a gas stream. The conduit 12 may be the main pipeline through which a gas stream is transported to a distribution system or other ultimate destination, or the conduit 12 may be an ancillary pipeline connected to the main pipeline, and through which all or part of the gas stream may be caused to pass during periods when a liquefied cryogenic fluid stream is to be vaporized and combined therewith.

A conduit 14 is connected to the conduit 12 and connected to a conventional gas compressor or blower 16. The discharge of the gas compressor 16 is connected by a conduit 18 to the heating coil 20 of a conventional gas heater 22. The heater 22 may be any suitable conventional gas stream heater, but preferably in a gas fired heater of the type described and claimed in US. Pat. No. 2,993,479. A conduit 24 is connected to the discharge of the heating coil 20 of the heater 22 and to the inlet of a contactor apparatus, generally designated by the numeral 26. As will be described further hereinbelow, the contactor apparatus 26 is of a design such that a stream of llquefied cryogenic fluid entering the apparatus through a conduit 32 connected thereto is mixed with and intimately contacted by a heated gas stream entering the apparatus 26 through conduit 24. The resultant mixture is withdrawn from the apparatus 26 through a conduit 30 connected to the outlet of contactor apparatus 26. The conduit 30 is connected to the conduit 12 at a point downstream of the conduit 14. For convenience, the conduits 14, 18, 24 and 30, and the compressor 16, heater 22 and contactor apparatus 26 of the system 10 is referred to herein as the heating circuit.

A conventional cryogenic fluid storage tank 34 is provided, and a conduit 36 connects the storage tank 34 to a liquefied cryogenic fluid pump 38, which may be any conventional pump suitable for pumping low temperature cryogenic fluids. The discharge of the pump 38 is connected to the conduit 32 which is in turn connected to the contactor apparatus 26 of the heating circuit of the system 10.

In operation of the system 10 illustrated in FIG. 1, a gas stream, to which vaporized cryogenic fluid is to be combined, is passed through the conduit 12 and a portion of the gas stream flows from the conduit 12 into the heating circuit of the system 10 through the conduit 14 attached thereto. The compressor 16 may be any conventional gas compressor or blower which will pump a predetermined volume of gas through the heating circuit of the system 10, and simultaneously raise the pressure thereof a predetermined amount. Specifically, the compressor 16 is of a design and type which raises the pressure of the gas stream an amount suflicient to cause it to flow through the heating clrcuit of the system 10 without incurring an overall pressure drop in the gas stream. For example, assuming that the pressure level of the gas stream passing through the conduit 12 is 500 p.s.i.g. and the pressure drop of a predetermined volume of gas passing through the heating circuit is 10 p.s.i., the compressor 16 is designed to elevate the pressure of the volume of gas to a level of approximately 510 p.s.i.g. Thus, by reason of the compressor 16, a portion of the gas stream passing through the condu1t 12 may be caused to flow through the heating circuit of the system 10 without incurring a substantial pressure reduction in the gas stream.

The storage tank 34 contains a reservoir of liquefied cryogenic fluid. A stream of liquefied cryogenic flllld is conducted from the tank 34 by the conduit 36 to the pump 38. The discharge of the pump 38 is led by a conduit 32 to the cryogenic fluid inlet connection of the contactor apparatus 26. As will be understood, the cryogenic fluid pump 38 is of a design such that the pressure level of the stream of liquefied cryogenic fluid passing mto conduit 32 is elevated to a level so that it is in ected mto the contactor apparatus 26 through the cryogemc fluid inlet connection thereof. A conventional flow control assembly 40 is disposed in the conduit 32 for controlling the flow of liquefied cryogenic fluid passing mto the contractor apparatus 26.

The portion of the gas stream passing through the heating circuit of the system 10 is heated by the heater 22 a predetermined amount. Specifically, a quantity of heat is transferred to the gas stream which is equal to the quantity of heat required to vaporize the stream of liquefied cryogenic fluid entering the contactor apparatus 26 and superheat the vaporized cryogenic fluid to a desired combined stream temperature. The heated gas stream passes through the conduit 24 into the contactor apparatus 26 where it intimately contacts liquefied cryogenic fluid injected therein. While within contactor apparatus 26, heat is transferred from the heated gas stream to the liquefied cryogenic fluid causing it to be vaporized and mixed with the gas stream. The mixture then passes from the contactor apparatus 26 into the conduit 30. The mixture is led by the conduit 30 into the conduit 12 where it is combined with the remaining portion of the inlet gas stream passing therethrough. A conventional temperature controller and fuel control valve assembly 42 is provided which senses the temperature of the gas mixture passing through the conduit 30 and functions to regulate the quantity of fuel passing through a conduit 41 which is connected to the burner or burners (not shown) associated with the heater 22. That is, if the temperature of the gas mixture passing through the conduit 30 is below a preselected desired temperature, additional fuel is caused to enter the burner of heater 22 which in turn causes more heat to be transferred into the gas stream passing through the heating coil 20 thereof, and vice versa. Thus, the rate of flow of the liquefied cryogenic fluid being vaporized and combined with the gas stream may be increased or decreased as desired and the temperature controller 36 will automatically cause the amount of heat being transferred to the gas stream to be increased or decreased proportionately.

The particular flow rate of gas passed into the heating circuit of the system 10 will depend on various factors such as the flow rate of liquefied cryogenic fluid to be vaporized, the desired combined stream outlet temperature, and optimum economics relating to the system. As will be understood, conventional engineering calculations may be employed to determine optimum flow rates, temperatures and sizes of apparatus required.

Referring now to FIG. 2, an alternate system for carrying out the improved method of the present invention is illustrated, generally designated by the numeral 50. The system 50 is similar to the system 10 shown in FIG. 1 and includes a conduit 52 for receiving and conducting a gas stream to which a stream of liquefied cryogenic fluid is to be combined. The system 50 further includes a heating circuit comprised of a conduit 54 which is connected to a conduit 52 and to a compressor or blower 56. The compressor or blower 56 is driven by a conventional gas turbine 58. A conduit 60 connects the discharge of the blower 56 to a coil 62 which is disposed in heat exchange relationship with the exhaust gases generated in the gas turbine 58. A conduit 64 connects the outlet of the heat exchanger coil 62 to a heating coil 66 disposed within a conventional gas fired heater 68. The discharge of the heating coil 66 of the heater 68 is connected by a conduit 70 to a contactor apparatus of the same type and design described above, generally designated by the numeral 72. The discharge connection of the contactor apparatus 72 is connected to a conduit 74 which is in turn connected to the conduit 52 at a point downstream of the conduit 54.

A liquefied cryogenic fluid storage tank 76 is provided connected to a conventional liquefied cryogenic fluid pump 78 by conduit 80. The discharge of the pump 78 is connected to the contacting apparatus 72 by conduit 82. A liquefied cryogenic fluid flow control assembly generally designated by the numeral 84 is provided for controlling the rate of flow of liquefied cryogenic fluid to the contactor apparatus 72, and a conventional temperature controller and fuel control valve assembly 86 is provided which functions in the same manner as the temperature controller and fuel valve assembly 42 described above.

The system illustrated in FIG. 2 operates in the same manner as the system illustrated in FIG. 1 and described above except that the blower 56 is driven by a conventional gas turbine 58. As will be understood by those skilled in the art, a gas turbine produces a large volume of hot exhaust gases which are normally vented to the atmosphere. In the system illustrated in FIG. 2, these exhaust gases are passed in heat exchange relationship with the gas stream passing through the heating circuit of the system 50 prior to passing the gas stream into the heating coil 66 of heater 68. Thus, the gas stream is preheated in the heat exchanger coil 62 and then heated further in heating coil 66 of the heater 68. In applications of the present invention where electric power is not available or other economic factors dictate the use of gas as a source of power for driving the compressor 56, the use of the system 50 is economically advantageous.

In both of the systems illustrated in FIGS. 1 and 2 and described above, a portion of the mixture of the gas stream and vaporized cryogenic fluid from the heating circuit may be recycled through the heating circuit. That is, referring to FIG. 1, a conduit 28 may be provided connected to the conduit 30 and connected to the conduit 14 upstream of the compressor 16. This arrangement is particularly advantageous in applications where large volumes of liquefied cryogenic fluids are to be vaporized and combined with a relatively small gas stream.

Referring now to FIG. 3, a contactor apparatus generally designated by the numeral 100 is illustrated in detail. As will be understood, the contactor apparatus 100 is identical to the contactor apparatus 26 and 72 shown in FIGS. 1 and 2 and described above. While various types of contactor apparatus may be employed in the present invention, such as the apparatus disclosed in my copending application Ser. No. 6,889 filed Jan. 29, 1970, it has now been found that a contactor apparatus of the type shown in FIG. 3 is highly effective and economically manufactured. The contactor apparatus 100 basically comprises a first conduit member 102 having a conventional flanged inlet connection 104 at the forward end 106 thereof. The rearward end 108 of the conduit 102 includes a conventional blind flange assembly 112 welded thereto through which a liquefied cryogenic fluid inlet nozzle 110 passees. The nozzle 110 is comprised of a short length of pipe having an open forward end 111 and a conventional flange connection 113 at the rearward end 115 thereof. The nozzle 110 passes through and is sealingly welded to the blind flange member of flange assembly 112. The cryogenic fluid nozzle 110 extends within the conduit 102 a short distance, and a second conduit member 116 is connected to the conduit 102, the center line of the conduit 116 being positioned perpendicular to the center line of the conduit 102. A conventional flange connection 118 is attached to the lower end of the conduit 116.

In operation of the contactor apparatus 100, a heated gas stream passes into the contactor apparatus through the forward end 106 of the conduit member 102. A stream of liquefied cryogenic fluid to be vaporized and combined with the gas stream passes through the nozzle and is sprayed from the nozzle 110 within the conduit 102 in a direction countercurrent to the direction of the heated gas stream passing therethrough. The liquefied cryogenic fluid is intimately contacted by the heated gas stream within the conduit 102 causing heat to be transferred thereto which brings about the vaporization of the cryogenic fluid. The vaporized cryogenic fluid passes through the conduit 116 and out of the contactor apparatus 100. While the contactor app-aratus'100 is formed of materials resistant to cryogenic fluid temperatures, such as stainless steel or aluminum, its relatively small size and simple design makes it more economical to manufacture than other types of apparatus heretofore used.

Thus, an improved method of vaporizing and combining a liquefied cryogenic fluid stream with a gas stream is provided which may be carried out in relatively simple and inexpensive apparatus, and wherein an overall pressure reduction of the gas stream does not result. While a blower or compressor is employed to provide the driving force for causing a portion of the gas stream to be circulated through the heating circuit of the present invention, the horsepower requirements for driving the compressor or blower are inconsequential as compared to that required to raise the pressure of the entire gas stream to which the liquefied cryogenic fluid is added.

The present invention is, therefore, well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments of the invention are given for the purpose of disclosure numerous changes can be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed therein.

What is claimed is: 1. An improved method of combining a liquefied cryogenic fluid stream with a gas stream for transport to a point of use comprising the steps of:

dividing the gas stream into first and second portions; elevating the pressure of the first portion of said gas stream an amount sufficient to cause the first portion to pass through a heating circuit and recombine with the second portion of said gas stream without incurring a substantial pressure drop in said gas stream;

heating the first portion of said gas stream within said heating circuit so that a quantity of heat is added thereto substantially equal to the heat required to vaporize and superheat said stream of liquefied cryogenic fluid to the desired temperature of the combined first portion of said gas stream and vaporized cryogenic fluid; injecting said stream of liquefied cryogenic fluid directly into the heated first portion of said gas stream within the heating circuit so that the liquefied cryogenic fluid is vaporized, superheated and mixed with the first portion of said gas stream; automatically controlling the heating of the first portion of said gas stream in predetermined relationship with the temperature of the mixture of the first portion of said gas stream and vaporized cryogenic fluid so that said mixture has a desired temperature; and

combining the mixture of the first portion of said gas stream and vaporized cryogenic fluid with the second portion of said gas stream.

7 2. The method of claim 1 wherein-the gas stream is natural gas.

3. The method of claim 2 wherein the liquefied cryogenic fluid is liquefied natural gas.

4. The method of claim 1 which is further characterized to include the steps of:

dividing said mixture of the first portion of said gas stream and vaporized cryogenic fluid into first and second portions; combining the first portion of said mixture with the first portion of said gas stream; and recycling the second portion of said mixture within said heating circuit. 5. The method of claim 4 wherein the gas stream is natural gas.

6. The method of claim 5 wherein the liquified cryogenic fluid is liquefied natural gas.

References Cited UNITED STATES PATENTS Dunkak 13790 X King 48 -l X Colucci 261--16 Nelly, Jr. et a1. 48-190 X Hasche 48-190 X Stevens 48l90 X Meiller et al. 48-490 Loprete 60--39.7 X Melenric 6039.71 X Stark et a1. 48-190 JOSEPH SCOVRONEK, Primary Examiner U.S. C1. X.R.

48-180 R, P, 191, 196 R; 137-7, 89 

